Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$18.75	12.769%	$21.1442	$21.14	$21.15	$21.10
Purchase #2	$237.39	12.432%	$266.9023	$266.90	$266.90	$266.90
Purchase #3	$112.38	3.662%	$116.4954	$116.50	$116.50	$116.50
Purchase #4	$65.52	6.435%	$69.7362	$69.74	$69.75	$69.70
Purchase #5	$99.31	12.721%	$111.9432	$111.94	$111.95	$111.90
Purchase #6	$23.30	8.786%	$25.3471	$25.35	$25.35	$25.30
Purchase #7	$148.49	5.504%	$156.6629	$156.66	$156.65	$156.70
7 purchase totals =	$705.14		$768.2313	$768.23	$768.25	$768.10